The invention relates to a special section tube for the production of readily assembled and dismantled framework structures, in particular for use at fairs and exhibitions, with a plurality of undercut longitudinal grooves on the outside, which are engaged by the joining parts of clamping elements with a rectangular outer cross-section to connection with further sectional parts.
Special section tubes of this type are known for example in German DE-AS No. 29 41 008. The tubes generally are hollow, defining a cylindrical, longitudinally centrally arranged cavity that is relatively small compared with the external dimensions of the tube. A plurality of longitudinal chambers are arranged in a circumferentially spaced manner around the tube circumference. The chambers are open to the outside by means of longitudinal grooves and are adapted to receive so-called tie bars which clamp into the grooves. Such clamping elements have an approximately square block-shaped external configuration and may be installed into section supports also having a rectangular cross-section. The clamping elements are held in position within the section supports by means of bolt heads protruding outwardly through bore holes in the supports and actuable from the outside, in order to pressure the tie bars outwardly and to pull them to the rear. It is a disadvantage of these known configurations that in this manner only rectangularly-shaped section supports may be connected with the special section tubes, and that such tubes may not be assembled to each other by means of the clamping elements, or at least not in a simple fashion.
It is also known, for example in U.S. Pat. No. 3,574,367, to use square section tubes similar to the afore-mentioned type exclusively as parts for the assembly of a frame, which also may be assembled with each other by means of clamping elements equipped with spreading parts. However, the variational possibilities and also the esthetic appearance of the afore-mentioned special section tubes with eight, but at least six edges, cannot be attained by these configurations.
It is an object of the present invention to provide special section tubes of the above-mentioned type so that the mutual joining of several section tubes may be effected by means of the clamping elements with the option of numerous variations, but that in spite of this, the connection of other sectional supports, as in the state of the art, is not excluded.